1. Field of the Invention
The present invention relates to an electroluminescent arrangement containing one or more organic layers, at least one of which obtained by thermal-or radiation-induced crosslinking and contains at least one charge-transporting compound which can carry crosslinkable groups per layer, wherein one of the layers is completely or partially composed of a cross-linkable fluorescent compound, and the compound emits fluorescent light in the wavelength range from 400 to 800 nm.
2. Description of the Background
On application of an electrical voltage, an electroluminescent (EL) arrangement emits light with a flow of current. Such arrangement have long been known in industry under the name light emitting diodes (LEDs). The emission of light occurs when positive charges (holes) and negative charges (electrons) combine with emission of light.
The LEDs usually used in industry all consist predominantly of inorganic semiconductor materials. However, EL arrangements whose essential components are organic materials have been known for a few years.
These organic EL arrangements contain, as a rule, one or more layers of organic charge-transporting compounds. The structural principle is shown in the figure. The numbers 1 to 10 have the following meanings:
1 substrate PA1 2 base electrode PA1 3 hole-injecting layer PA1 4 hole-transporting layer PA1 5 emitter layer PA1 6 electron-transporting layer PA1 7 electron-injecting layer PA1 8 top electrode PA1 9 contacts PA1 10 encapsulation
is structure represents the most general case and can be simplified by omitting individual layers so that a layer performs a plurality of functions. In the simplest case, an EL arrangement consists of two electrodes between which an organic layer which performs all functions, including that of the emission of light, is present. Such systems based on poly-p-phenylenevinyls! are described, for example, in WO 9013148.
The literature describes a large number of organic compounds which transport charges (holes and/or electrons). Low molecular weight substances which are applied, for example, by vapor deposition under greatly reduced pressure are predominantly used. For example, the publications EP-A-387715 and U.S. Pat. Nos. 4,53,9507, 4,720,432 and 4,769,292 give a good overview of the classes of substances and their use. In principle, it is possible to use all substances which are known in electrophotography to be photoconductors.
The common feature of all these EL arrangements which are based on low molecular weight compounds is that they do not have a sufficient operating life. During operation, the organic light emitting diodes become very hot (&gt;100.degree. C.), and this leads to a change in the layers including their destruction, so that reduced performance or complete loss of function is encountered.
These problems were set to occur to a lesser extent when polymers were used in EL arrangements. However, layers which contain polymer have not been widely described. Thus, Japanese Preliminary Published Application JP 4028197 describes, for example, an EL arrangement which contains polyvinylcarbazole as a component of the emitter layer. Soluble polymers, such as polyvinylcarbazole, are applied by casting or spin-coating using dilute solutions. The disadvantage of this process is that a plurality of layers cannot be applied in this way since the solvent for the second layer superficially dissolves or at least superficially swells the first layer. This then leads to mixing of the two layers at the interface and hence to a reduction in efficiency. These problems are described in detail in U.S. Pat. No. 4,539,507.
It should also be noted that the thermal stability of polymer layers are limited not only chemically (decomposition) but also physically by their glass transition temperature or melting point.
Further examples of the use of polymers in EL arrangements are polyp-phenylenevinyls! (PPV) and polyimides. The use of PPV in EL arrangements is described in EP-A-443861, and in WO-A-9013148, 9203490 and 9203491. The high thermal stability of PPV, which is also insoluble, may be mentioned as an advantage.
Polyimide layers are obtained by vapor deposition of corresponding comonomers under greatly reduced pressure and subsequent thermal formation of the polyimide (cf. EP-A-449125). These polymers are likewise insoluble.
For applications in the EL sector (in particular displays), this insolubility is considered a disadvantage because it excludes the possibility of photostructuring. Moreover, the thermal treatment of the substrates, which treatment is required for the preparation of the polymers, limits the choice to substrates which are stable at high temperatures, for example glass.